Role of ligands in the stability of B_nX_n and CB_n-1X_n (n = 5-10; X = H, F, CN) and their potential as building blocks of electrolytes in lithium ion batteries

Stabilizing small multiply charged negative ions in the gas phase has been of considerable interest in recent years. B₁₂H₁₂^2- is one of the most well-known dianions which is stable against auto-detachment of its second electron in the gas phase by 0.9 eV, whereas B_nH_n^2- with n < 12 is unstable. Using density functional theory, we have examined systematically the role of ligands in stabilizing smaller mono- and di-anions of B_nX_n and CB_n-1X_n (n = 5-10; X = H, F, CN). We show that the stability of the negative ions of these complexes increases with the electron affinity of the ligand and B_n(CN)_n^2- can even be stable against electron emission for n ≥ 5. We also show that CB_n-1(CN)_n^2- is stable against electron emission for n ≥ 8, even though these moieties contain one electron more than needed to satisfy the Wade-Mingos rule. We have examined the potential of these stable negative ions as building blocks of electrolytes in Li-ion batteries. By calculating the binding energies between the CB_n-1X_n^1-,2- and Li⁺, we find that some of these clusters may even outperform CB₁₁H₁₂^- as electrolytes in metal-ion batteries.